Measuring groundwater permeability (or transmissivity profiles) in fractured rock has traditionally been done by diamond coring, assessing where major fracture sets of interest are by logging core, and then running straddle packers at discrete elevations to characterise the formation. An alternative method which is typically much faster and therefore more cost effective has been developed using Flexible Liner Underground Technologies (FLUTe).
FLUTe liners are made of a high strength polyurethane covered nylon which makes them impermeable and completely water tight. The liners are installed by ‘everting’ (the process of turn something inside out) by filling the liner from the surface – it is a simple recipe of ‘just add water’!
As the everting blank liner is installed into an open borehole, groundwater in the borehole is forced from the hole into the formation by whatever flow paths are available (e.g., fractures, permeable beds, solution channels, etc.). Figure 1 shows the everting liner as it propagates down the open hole.
When the liner begins its descent in the hole, all of the flow paths are open and the descent rate is highest (Figure 2). As the liner progressively covers individual flow paths (e.g. water bearing fractures etc.), the liner descent rate decreases. From a plot of the decreasing velocity with depth, a transmissivity profile can be constructed for the hole (Figure 3).
In most cases, the FLUTe Transmissivity Profiler™ can map all the significant flow paths in the hole in less than 10 percent of the time required to do the same mapping with a straddle packer (as holes can be drilled using rotary air rather than diamond core) – an advantage when trying to quickly and cost effectively understand the hydraulic conditions at your site.
For more information contact Mike at Matrix Drilling on 1300 662 565, or visit www.flut.com